View source for Platform/Input/Touch

This page describes the state of touch input and events on all tier-1 platforms. On this page "input" will refer to the input events that Gecko receives from the OS, and "events" will refer to DOM events dispatched into web content.

In general touch input received from the user can be dispatched to web content in the form of (a) touch events (b) pointer events and (c) mouse events.

Touch events are covered by [http://www.w3.org/TR/touch-events/]. In general these are widely used on the web but have main thread dependencies which makes them unsuitable for async touch-based pan/zoom. For backwards compatibility we need to support these but going forward we would like to use pointer events instead and deprecate touch events.

Pointer events were proposed by Microsoft. Initially it had support from Google but then they changed their mind and as of this writing they do not plan to support it. Microsoft is trying to push pointer events and people from MS Open Tech are actively implementing pointer events support in Gecko. In Gecko we would like to have pointer events and would also like Google to support them for better interoperability. There is some code in nsPresShell in Gecko which can generate and dispatch appropriate pointer events based on touch/mouse input.

Mouse events are also dispatched for backwards compatibility with non-touch-aware web content. The only cases where mouse events need to be dispatched to content are when the user does a "tap" and the resulting touch events are not prevent-defaulted by web content. In this case three mouse events (mousemove, mousedown, mouseup) need to be dispatched to the point of the tap. A fourth event (click) is created by the EventStateManager from the mousedown/mouseup pair. Note that there must be some sort of gesture detection that happens somewhere in order to determine that a sequence of touch input corresponds to a "tap".